The invention relates to an air-compressing fuel injection internal-combustion engine with an exhaust treatment device, to which reduction agents for the reduction of nitrogen oxides can be fed.
EP 0 488 386 A1 discloses an internal-combustion engine with an exhaust treatment device reducing nitrogen oxides and with a fuel injection system comprising a high-pressure pump and at least one injection nozzle and with fuel or primary injection into the combustion chamber of the engine. For the purpose of nitrogen oxide reduction, liquid hydrocarbon taken from a reservoir is injected as a reduction agent by means of an additional injection nozzle opening out into the induction pipe. According to FIG. 7, this additional injection nozzle is connected by a line to a main injection nozzle, provided for the primary injection. In this case, the main injection nozzle and additional injection nozzle are intended for different cylinders of the engine.
The primary injection into the combustion chamber of the engine, intended for the combustion, takes place through the main injection nozzle, while the secondary or additional injection, serving for nitrogen oxide reduction, takes place into the air induction pipe through the additional injection nozzle at the point in time of the overlap top dead center, at which inlet valve and outlet valve are simultaneously opened for a short time.
An object of the invention is to use measures which are more simple, constructionally less demanding and more effective with regard to consumption on an internal-combustion engine of the generic type to meet also the more stringent requirements in future with regard to the percentages of pollutants in the exhaust, in particular nitrogen oxides.
This object is achieved according to the invention by providing an arrangement wherein the primary injection for combustion and the secondary or supplemental injection for reduction of nitrogen oxides is made through the same injection nozzle at respective times during the operating cycle.
Beneficial further developments of the invention are further specified in the subclaims.
Due to the fact that not only the primary injection intended for combustion is performed into the combustion chamber of the engine, but also a secondary or additional injection, effecting the rapid activation of the exhaust treatment device for the reduction in the nitrogen oxides, is performed as an early or late supplementary injection into this combustion chamber by a single fuel injection nozzle, a design which is significantly less demanding in terms of production and construction is achieved, in which the single fuel injection nozzle is actuated twice within an operating cycle of the engine with a defined time interval or, in the case of a design with pre-injection and main injection, is actuated three times.
The additional injection as an early supplementary injection takes place in the region of the end phase of the combustion between 20.degree. and 80.degree. after ignition top dead center; the fuel, for example diesel fuel, as an "early" supplementary injection thus occurs at a point in time at which the combustion from the primary injection is at least largely complete. The combustion chamber temperatures must be high enough that the amount of fuel to be supplementarily injected burns as completely as possible. This additionally introduced amount of fuel serves exclusively for the desired increasing of the exhaust temperature before the catalytic converter.
On the other hand, the additional injection as a late supplementary injection does not participate in the combustion and commences at a point in time between 80.degree. after ignition top dead center and the bottom dead center region, at which the fuel does not burn, but evaporates, cracks and mixes with air and the combustion gases, the NO.sub.x molecules being reduced whilst still in the combustion chamber in the hot gas and flowing to the exhaust treatment device, a denox catalytic converter, for example formed by a zeolith or perovskite catalyst.
In the denox catalytic converter, reactions form between the NO.sub.x molecules and the highly reactive hydrocarbon fractions or readily reacting radicals, which results in reduction of the NO.sub.x molecules in the nitrogen and oxygen. The additional injection is appropriate in particular in the case of injection systems which operate on the basis of the common-rail principle, since there are always high pressures available in the accumulator system, which have advantageous effects on the quality of atomization even in the case of the additional injection.
However, so-called electronically actuated unit fuel injectors can also be used for the additional injection. The additional injection is suitable both for pre-chamber and swirl-chamber internal-combustion engines and for direct-injection internal-combustion engines and can also be used in the case of injection systems with pre injection and main injection.
Due to the nitrogen oxide-reducing measures in the case of the late supplementary injection, important parameters can be freely set or selected, such as the amount of reduction agent, the point in time of its introduction and the level of the pressure, whereby the preparation of the reduction agent can be optimized with regard to the rates of reduction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.